U.S. patent number 4,450,431 [Application Number 06/267,258] was granted by the patent office on 1984-05-22 for condition monitoring system (tire pressure).
Invention is credited to Peter A. Hochstein.
United States Patent |
4,450,431 |
Hochstein |
May 22, 1984 |
Condition monitoring system (tire pressure)
Abstract
A monitoring system for monitoring the condition in a vehicle
wheel mounted tire. The system includes first and second LC
circuits disposed within the tire and interconnected by a diode
multiplier in series with a pressure switch. An exciter establishes
an energetic electromagnetic field of a first frequency such that a
first LC circuit is resonant at the same first frequency. This
first frequency is converted into energy of a second frequency by a
harmonic multiplier diode and is impressed upon a second LC circuit
which is resonant at the second frequency, the second frequency
being either an even or odd harmonic of the first (exciting)
frequency. A receiver tuned to the second frequency interrogates
the second LC circuit for presence of harmonic energy at the second
frequency. A pressure switch opens when the tire pressure falls
below a predetermined pressure which prevents activation of the
second LC circuit so that the receiver will not sense the second
frequency to which the second LC circuit is resonant, in which case
there is provided an indication that the tire pressure is below the
desired pressure. A scanner scans the receiver successively from
one tire to another of a vehicle.
Inventors: |
Hochstein; Peter A. (Sterling
Heights, MI) |
Family
ID: |
23018006 |
Appl.
No.: |
06/267,258 |
Filed: |
May 26, 1981 |
Current U.S.
Class: |
340/447; 342/50;
340/539.1; 340/505; 340/870.31 |
Current CPC
Class: |
B60C
23/0428 (20130101); B60C 23/0449 (20130101) |
Current International
Class: |
B60C
23/02 (20060101); B60C 23/04 (20060101); B60C
023/00 () |
Field of
Search: |
;340/58,572,870.31,539,505 ;200/61.22,61.25 ;73/146.5
;343/6.5R,6.5SS,6.8R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Assistant Examiner: Nowicki; Joseph
Attorney, Agent or Firm: Milton, Jr.; Harold W.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A tire condition monitoring system for monitoring the condition
of a wheel mounted tire comprising; exciter means for establishing
an electromagnetic energy field having a first frequency, passive
converter means responsive to said first frequency for creating
energy having a second frequency, sensing means for changing
amplitude of said energy at said second frequency by said converter
means in response to a predetermined change of the tire condition,
receiver means responsible to said energy at said second frequency
for providing an indication regarding said energy at said second
frequency, said converting means including harmonic multiplier
means for making said second frequency a harmonic of said first
frequency, said exciter means being inductively coupled to said
converter means through a magnetic field, said receiver means
including an E-field antenna for receiving an E-field from said
converter means.
2. A system as set forth in claim 1 wherein said converter means
includes a first passive LC circuit coupled inductively to said
exciter means and resonant to said first frequency and a second
passive LC circuit resonant to said second frequency, said harmonic
multiplier means interconnecting said first and second LC circuits
for making said second frequency a harmonic of said first
frequency, said first LC circuit being grounded for propagating the
E-field from said second LC circuit, said sensing means being
disposed for disabling said second LC circuit.
3. A system as set forth in claim 2 wherein said sensing means
comprises a pressure switch which opens to dissable the converter
circuit in response to the tire pressure falling below a
predetermined pressure and which closes to enable the converter
circuit in response to pressure at and above said predetermined
pressure.
4. A system as set forth in claim 1 wherein said exciter means is
shielded against E-field propagation.
5. A system as set forth in claim 1 including a plurality of said
converter means, each having the same respective first and second
frequencies, and scanner means for serially detecting the E-field
from the respective converter means through said E-field
antenna.
6. A system as set forth in claim 1 including a plurality of said
converter means, and wherein said receiver means includes scanner
means for serially interrogating said respective converter means
one after the other.
7. A system as set forth in claim 6 wherein said first frequencies
are the same for each of said converter means and said second
frequencies are the same for each of said converter means.
8. A tire condition monitoring system for monitoring the condition
of a wheel mounted tire comprising; exciter means for establishing
an electromagnetic energy field having a first frequency, passive
converter means responsive to said first frequency for creating
energy having a second frequency, sensing means for changing
amplitude of said energy at said second frequency by said converter
means in response to a predetermined change of the tire condition,
receiver means responsive to said energy at said second frequency
for providing an indication regarding said energy at said second
frequency, said converting means including harmonic multiplier
means for making said second frequency a harmonic of said first
frequency, said converter means including a converter circuit and
said sensing means comprising a pressure switch in said converter
circuit for disabling said circuit in response to the tire pressure
falling below a predetermined pressure for terminating the creation
of said energy at said second frequency in response to an undesired
low pressure, indicator means responsive to said receiver means for
producing an alarm upon the discontinuance of said receiver means
sensing said energy at said second frequency and an alarm upon
initiation of said interrogation means sensing said energy at said
second frequency so that an alarm is provided when tire pressure
falls below the predetermined pressure and an alarm is provided
when the tire pressure rises to the predetermined pressure.
9. A method of monitoring the condition of a vehicle wheel mounted
tire comprising the steps of; establishing an inductive coupling
with a field of electromagnetic energy having a first frequency,
creating E-field energy having a second frequency which is a
harmonic of the first frequency in response to the inductive
coupling of said first energy, changing said E-field energy at said
second frequency in response to a predetermined change of the tire
condition, and interrogating for the existence of said E-field
energy at said second frequency.
10. A method as set forth in claim 9 further defined as creating a
first energy field at a plurality of wheels on a vehicle and
serially scanning the creation of the energy at the second
frequency at each wheel one after the other to serially determine
the presence of energy at the second frequency at each wheel.
11. A method as set forth in claim 9 further defined as shielding
of E-field energy in the establishment of the inductive
coupling.
12. A method of monitoring the condition of a vehicle wheel mounted
tire comprising the steps of; establishing a field of
electromagnetic energy having a first frequency, creating energy
having a second frequency which is a harmonic of the first
frequency in response to said first energy, changing said energy at
said second frequency in response to a predetermined change of the
tire condition, interrogating for the existence of said energy at
said second frequency, sensing the tire pressure, terminating the
creation of energy at the second frequency in response to the tire
pressure being below a predetermined pressure, providing an alarm
upon the discontinuance of energy at the second frequency and
providing an alarm upon the initiation of energy at the second
frequency so that an alarm is provided when the tire pressure falls
below the predetermined pressure and an alarm is provided when the
tire pressure rises to the predetermined pressure.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The subject invention relates to a method and system for monitoring
the condition of a vehicle wheel mounted tire such as the pressure
or temperature within the tire.
(2) Description of the Prior Art
For some time there has been interest in monitoring the air
pressure in a pneumatic tire. Because an important factor governing
the useful service life of a pneumatic tire is correct inflation
pressure, there has been significant interest with truck tires
because of their relatively high replacement cost. There is now,
however, also significant interest in monitoring the tire inflation
pressures on passenger cars because correct inflation pressures
significantly improve fuel economy by decreasing tire rolling
resistance.
Many systems have been proposed to continuously monitor tire
pressure on a vehicle but none have been widely adopted because of
difficulties with either cost, complexity, reliability or a
combination of these factors.
The prior systems have either been mechanical or electrical with
the mechanical systems having been virtually eliminated from
consideration. Electrical systems have included a battery powered
wheel mounted radio transmitter or a passive circuit, energy
absorbing type or an induction or transformer type. The battery
type is such that the system draws power from the battery only when
a decrease in pressure or rise in temperature occurs to power the
transmitter. These systems have not been widely accepted because
they are not fail-safe in that, if a malfunction occurs in the
system, there is no indication whatsoever. In a fail-safe system,
the monitor must be active and self-checking until a fault is
sensed such as a decrease in the tire pressure below a
predetermined pressure. If a battery were to be utilized in such a
system it would have to be continually recharged because the system
would be providing a signal at all times except when a fault is
sensed.
Passive circuits which have been utilized to sense tire pressure
have not had the desired sensitivity and have inherent coupling
problems. Furthermore, coupling to the antenna in such systems is a
function of the rotational position of the wheel, thereby allowing
only intermittent sensing. Reliable pressure sensing on a nonmoving
vehicle is, therefore, impossible.
SUMMARY OF THE INVENTION
The invention is a tire condition monitor system for monitoring the
condition in a vehicle wheel mounted tire. The system includes an
exciter means for establishing an electromagnetic energy field
having a first frequency and a passive converter means responsive
to the first frequency creates energy having a second frequency.
The energy at the second frequency is changed in response to a
predetermined change of the tire condition and a receiver means is
responsive to the energy signal at the second frequency for
providing an indication regarding the energy signal at the second
frequency. The converter means includes multiplier means for making
the second frequency a harmonic of the first frequency.
PRIOR ART STATEMENT
The U.S. Pat. No. 3,723,966 granted Mar. 27, 1973 to Mueller et al
discloses a passive circuit-type tire monitor including a passive
converter circuit having a pressure switch in the circuit. A
transmitter transmits to the passive circuit which, in turn,
absorbs some of the transmitted signal by being resonant at the
same frequency as that of the transmitted signal. The received,
measured, signal is actually the transmitted signal energy minus
that energy absorbed by the passive circuit which is resonant to
the transmitter at the same frequency. The problem with such a
system is the separation of the relatively large transmitted signal
from the relatively small absorbed signal.
Another monitoring system is disclosed in U.S. Pat. No. 2,274,557
granted Feb. 24, 1942 to Morgan et al. There is disclosed therein a
system employing three circuits with the second responsive to the
first to provide an indication in the third circuit. Again, the
problem is the lack of separation between the signals.
Yet another system is disclosed in U.S. Pat. No. 4,067,235 granted
Jan. 10, 1978 to Markland et al. wherein a tire pressure sensor
receives radiated energy and converts that energy into electrical
power to power a conventional transmitter circuit. A tank circuit,
rectifier, regulator oscillator and other components are used to
increase the output frequency as the tire pressure increases. A
relatively large amount of power is required for creating the
radiated energy received by the sensor. The subject invention
regains relatively low power for creating the radiated energy
which, in turn, is directly converted to a harmonic frequency of
the radiated energy.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the present invention will be readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
FIG. 1 is a schematic view of the subject system associated with a
vehicle;
FIG. 2 is a schematic view of one embodiment of the invention;
FIG. 3 is a schematic view similar to FIG. 2 but showing a second
embodiment;
FIG. 4 discloses an example circuit for the exciter;
FIG. 5 discloses an example circuit for the receiver; and
FIG. 6 discloses a logic and alarm circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A tire condition monitor system is shown in FIG. 1 for monitoring
the condition in all of the tires of a passenger vehicle. FIG. 2
illustrates a first embodiment of a basic system for monitoring the
condition of a singular vehicle wheel mounted tire. The invention
will be described as monitoring the pressure in a vehicle tire,
however, it will be appreciated that other conditions may be
monitored, such as temperature.
The monitoring system illustrated in FIG. 2 includes an exciter
means for establishing an electromagnetic energy field having a
first frequency. The exciter means comprises the exciter 10 and the
exciter antenna coil generally shown at 12. Preferably, a crystal
controlled conventional exciter 10 is used to generate 100 mW to
400 mW of radio frequency energy preferably at 9.5 MHz. The exciter
includes an oscillator, an amplifier and a harmonic filter to
attenuate undesired harmonics, all of which are conventional; value
of the components depends upon the frequency selected.
FIG. 4 illustrates a circuit for the exciter 10 which includes a
conventional oscillator, conventional amplifier and conventional
harmonic filter. The values for the various components utilized in
the circuit depend upon the frequency selected.
The output of the harmonic filter is matched to drive a low
impedance transmission line 14, typically 50 or 75 Ohms. The line
14 feeds an H-field radiator or antenna which is resonant at the
first frequency. The radiator antenna 12 consists of a resonant,
high Q, parallel tuned LC circuit consisting of a ferrite core coil
16 and a resonating capacitor 18, a specific example of which is
disclosed and claimed in applicant's co-pending application Ser.
No. 267,257, now abandoned filed concurrently herewith and assigned
to the assignee of the subject invention.
The monitoring system further includes a converter means generally
shown at 20, adapted to be carried by the vehicle wheel for
creating energy at a second frequency in response to the first
frequency. Also included is a sensing means in the form of switch
22 for causing a change in the amplitude of energy at the second
frequency in response to a predetermined change of the tire
condition, e.g., tire pressure.
The system further includes receiver or interrogation means
responsive to the energy at the second frequency for providing an
indication regarding the energy at the second frequency. The
receiver or interrogation means includes the receiver antenna coil
24 and the receiver 26. The receiver 26 may be any one of many
conventional well known receiver circuits, an example of such a
circuit being shown in FIG. 5. The receiver antenna coil 24 is
similar to the radiator antenna coil 12 which comprises a parallel
tuned LC network consisting of a ferrite core and coil 30 and a
resonating capacitor 32 with both circuits being grounded, as
indicated.
The system is characterized by the converter means 20 being
responsive to the first frequency of the field established by the
radiator antenna coil 12 and creating energy at a second and
different frequency, i.e., a harmonic of the first frequency. The
converter means 20 includes a first passive LC circuit, comprising
a coil 34 in parallel with a capacitor 36, and which is resonant to
the first frequency propagated by antenna coil 12. The converter
means 20 also includes a second passive LC circuit including the
coil 38 in parallel with the capacitor 40 and the resonant to the
second frequency which is different from the first frequency. The
converter means 20 includes a harmonic multiplier in the form of a
diode 42 for making the second frequency a harmonic of the first
frequency. The diode 42 interconnects the coils 34 and 38 of the LC
circuits. Preferably, the second LC circuit comprising the coil 38
and capacitor 40 is resonant at a second or third harmonic of the
frequency at which the first LC circuit (comprising the coil 34 and
capacitor 36) is resonant. The switch 22 is preferably a pressure
switch defining a sensing means which interconnects the first and
second LC circuits and is in series with the diode 42, although the
switch 22 may in some instances be in parallel with the diode 42.
The pressure switch 22 opens to disable the converter circuit in
response to the tire pressure falling below a predetermined
pressure. The pressure switch 22 will close to enable the converter
circuit in response to pressure at and above the predetermined
pressure. Thus, the pressure switch 22 is connected to the
converter means 20 for terminating the converting activity in
response to an undesired predetermined change of the tire pressure
condition.
The excitation of the converting circuit takes place at one
frequency while reception of the converted signal occurs at another
frequency which is harmonically related to the first frequency. The
system includes an indicator means comprising the logic and alarm
circuit 28 which is responsive to the receiver 26 of the
interrogation means for providing an alarm upon the discontinuance
of the interrogation means sensing the second signal from the
converting means 20. The indication means would also provide an
alarm upon the initiation of the interrogation means sensing the
second signal from the converter means 20. Thus, an alarm is
provided when the tire pressure falls below the predetermined
pressure and an alarm is also provided when the tire pressure rises
to the predetermined pressure, the circuit for accomplishing this
is explained hereinafter. This is an important feature and, should
the tire pressure fall below a predetermined desired level, an
alarm will be sounded for a short period of time whereas a light
will remain "on" indicating the low tire pressure. Upon reinflating
the tire to the proper or desired pressure, the alarm will again
sound and the light will be turned off eliminating the need for a
tire pressure gauge when inflating the tires. It is also important
that the system is fail-safe. The receiving antenna coil 24
constantly interrogates the converting circuit 20 for the second
frequency from the LC circuit 38, 40 which second frequency is in
existence so long as the pressure switch 22 is closed and there is
no other malfunction in any of the circuits. If, however, the
pressure switch 22 opens or there is another malfunction in the
system to discontinue the converted signal in the LC circuit 38,
40, the interrogating receiving antenna 24 will not sense that
second frequency of the second signal whereby an alarm is produced
to indicate a low tire pressure or that the system is not
functioning properly.
The embodiment of FIG. 3 includes the same or like components as
the system of FIG. 2 with those same or like components identified
by like reference numerals. The embodiment of FIG. 3 differs from
the embodiment of FIG. 1 in that the first LC circuit 34, 36 is
grounded at 44 to the vehicle wheel for propagating an E-field from
the LC circuit 38, 40. The interrogation means includes an E-field
antenna 46 for receiving the E-field from the second LC circuit 38,
40. This propagation which is characteristic of conventional radio
transmitting antennas, offers substantial advantages over the
H-field or magnetic field system of FIG. 2, the most significant of
which is that the E-field receiving antenna 46 may be disposed a
greater distance from the LC circuit 38, 40 of the converting
means. In the system of FIG. 3, the structure of the harmonic
generator coil 38 functions as a radiator or antenna and the steel
wheel of the vehicle functions as a grounded counterpoise.
The converting means 20 preferably takes the form of the coils 34
and 38 being disposed circumferentially about the rim of a
vehicular wheel and it is of the type more specifically disclosed
and claimed in applicant's co-pending application Ser. No. 267,261
filed concurrently herewith and assigned to the assignee of the
subject invention.
FIGS. 2 and 3 are illustrative of embodiments for monitoring the
tire pressure of a single wheel. FIG. 1 schematically shows a
system for serially or sequentially interrogating the various tires
of a passenger vehicle including a spare tire. An exciter or
radiating antenna 12 is disposed adjacent each tire and wheel
assembly as is a receiving antenna 24. The antennas 12 all send the
signal of the same frequency and all of the receiving antennas 24
are looking for the same harmonic of that frequency. A commutator
or scanner generally shown at 48 is utilized to sequentially
connect the exciter 10 to the respective antenna coils 12.
The matching network and combiner matches the impedance of the
outputs from the various receiver coils 24 to the receiver 26 for
efficient energy transfer, as is well known.
The decoding logic and alarm circuit 28 basically determines which
tire is being excited and sequentially connects the output of the
receiver to an indicator light for that tire and causes that light
to illuminate if there is no signal from the receiver, and further
causes an audible alarm.
As alluded to above, an advantage of the E-field system illustrated
in FIG. 3 is that a single E-field receiving antenna 46 may be
utilized to sense all of the converters associated with all the
vehicle wheels of a passenger car vehicle. In order to scan the
various wheels with the single antenna receiver in the E-field
system of FIG. 3, two scanners or commutators, such as that
schematically illustrated at 48, could be utilized to functionally
rotate in unison. The first scanner would sequentially connect the
output of the exciter 10 to the various exciter coils or radiating
antennas 12. In addition, however, there would be a second scanner
or commutator which functionally moves in unison therewith to
sequentially connect the appropriate indicator lamps to the output
of the receiver 26. Thus, when a converter in a given wheel is
being excited the receiving antenna 46 should be receiving a signal
which would be detected in the receiver 26. The two parallel
scanners or commutators would sequentially check each wheel and
tire assembly. The mechanical scanners are shown for simplicity;
normally, the scanning would be accomplished electronically. FIG. 6
discloses a logic and alarm circuit which scans electronically.
The circuit includes a clock oscillator 50 having a capacitor and
resistor which determine the frequency of the signal transmitted
along the clock line 52. The element 54 may be a CMOS 4093 Quad
2-input Nand gate. The element 56 is a binary three bit counter,
which may be a CMOS 74C161 programmable (.div.n) binary counter.
The element 58 may be a CMOS 4099 transparent addressable latch
which converts the binary three bit input to decimal outputs
continually scanning the five (5) outputs lines to a decoding
driver 60 which amplifies the various signals and sequentially
enables each of five (5) exciter coil circuits 62, one for each
wheel and a spare. For simplicity, only one of the five (5) exciter
coil circuits 62 is illustrated. Each circuit 62 has an input 64
from the exciter means 10 which passes through a diode acting as a
R.F. switch to the connection 66 to the exciter coil 12 adjacent
each tire, the exciter coil 12 establishing the energy field to
which the converter 20 is responsive.
The output of the binary counter 56 also drives a CMOS 4099 latch
68 which converts binary to decimal and scans the five decimal
positions but does not provide an output to anyone of its five
output lines unless enabled to do so by a signal from the Nand gate
70. The Nand gate 70 may be a CMOS 4093 Quad 2-input Nand gate. The
gate 70 has an input 72 from the receiver 26. When the signal from
the receiver is low or non-existent (as when the tire pressure
falls below the predetermined tire pressure), the gate 70 sends a
signal to the latch 68. The latch 68 is scanning the five tires in
synchronization with the latch 58, so that a single E-field antenna
would not receive a signal when the exciter coil for one of the
tires is producing an energy field but the converter 20 is not
responding. Therefore, the output from latch 68 would be for that
specific tire. The signal would drive a transistor array (e.g., of
the ULN 2003 Darlington type), which would illuminate the
appropriate one of five fault indicator lights or L.E.D.'s 74.
The output of the latch 68 will drive one of five edge detector
circuits 76.
Each edge detector circuit 76 includes two CMOS 4093 Quad 2-input
Nand gates 78 and 79 and produces an output signal in line 80 in
response to the initiation of the output from the latch 68 and also
in response to the discontinuance of the output from the latch 68,
as when the tire is inflated to the proper pressure.
The signal in line 80 actuates on Or gate 82 (e.g., CMOS 4071 Quad
2-input Or gate). The gate 82 triggers the monostable circuit 84
(including a CMOS 4528 monostable 86) which produces a pulse and
determines the width of the pulse, e.g., one second. This pulse
enables the audio alarm circuit 88. The alarm circuit 88 includes a
555 I.C. power oscillator 90 and audio transducer 92, the time
duration of the pulse from the monostable circuit 84 determining
the duration of the audio alarm. Because the edge detector circuit
76 produces a signal, both when the scanned position signal drops
out and falls back in, an alarm is produced both when the tire
pressure drops below the predetermined pressure and when the
pressure returns to the predetermined pressure.
The gate 82 has an input 94 which is from a second Or gate, the
same as 82, which second gate has an input from a second edge
detector circuit for a second tire and an input from yet a third
gate, the same as 82 for the third tire, and so on for the five
tires.
All of the voltage inputs (Vcc) are typically 6 volts, and are
regulated down from the vehicular power supply.
Thus, the logic and alarm circuit of FIG. 6 scans the various tires
and provides an indication by light when a tire condition is
unsatisfactory with the light indicating which tire and also
provides an audio alarm when the unsatisfactory condition occurs
and when it is corrected. The system is also fail-safe in that a
fault indication will occur if any active component fails in the
system.
Inoperable (burned out) indicator lamps would normally present a
reliability problem, however, the redundant audible alarm would
alert the driver to indicator malfunctions.
Furthermore, a manual push-to-test feature could check all
indicating circuits at operator command. Alternately, an automatic
self test circuit could check all indicators on initial power-up;
i.e., starting of the vehicle.
At 10 MHz, a practical radiator antenna coil 12 would consist of a
Q-2 ferrite core approximately 0.5" in diameter by 3.0" long with
six to eight turns of 0.10" wide copper tape tapped and fed at one
turn. In practice, one such coil is mounted in proximity to each
wheel rim (from 1" to 4" away) so as to induce the 10 MHz H-field
into the converter. To minimize electromagnetic interference due to
E-field propagation, each exciter coil 12 is shielded with a
special grounded electrostatic shield which surrounds the core.
In the form of the system shown in FIG. 2, r.f. current induced in
the first resonant circuits 34, 36 of the passive, wheel mounted
converter 20 causes harmonic energy to be created by diode 42
whereby the second resonant circuit 38, 40 of the converter (which
is turned to a harmonic of (f.sub.o) is excited. The excitation of
the second tuned circuit causes a second H-field to exist at the
harmonic multiple of the fundamental (f.sub.o) frequency. The
harmonic H-field is typically sensed by means of a pickup antenna
coil 24 located in proximity to the wheel (1" to 12" away).
Reception of second harmonic energy by the antenna is optimized by
once again using a high Q ferrite loaded coil and resonating
capacitor, sharply tuned to the desired harmonic (typically
2f.sub.o). In order to preserve the high loaded Q and to optimize
energy transfer, the ferrite antenna coil is properly tapped or
impedance matched to the low impedance transmission line which
conducts the received signal to an appropriate tuned receiver 26.
Using a receiving antenna coil similar in dimensions to the exciter
coil, r.f. levels of 10-20 uV were recovered at 2f.sub.o when
exciter power was nominally 300 mW and coil to wheel spacing was
maintained at two inches.
It has been emperically determined that in order to effectuate
maximum power transfer to and from the harmonic generator or
converter a high Q in both f.sub.o and nf.sub.o circuits is
critical; and careful impedance matching the harmonic multiplier
diode 42 to both coils 34 and 38 accomplishes this by optimum
connections of the diode 42 along the respective coils 34 and
38.
The invention has been described in an illustrative manner, and it
is to be understood that the teminology which has been used in
intended to be in the nature of words of description rather than of
limitation.
Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described.
* * * * *